Quinoline compounds have attracted the curiosity of chemists due to their fascinating biological potential. In the present study, the molecule 4-methylquinoline or lepidine is characterised by DFT/B3LYP with 6–311++G(d,p) basis set to explore the optimised structure. Experimental calculations are compared to the computed FT-IR, FT-Raman and UV–Vis spectra. Theoretical and observed spectra are found to be very comparable. Various polar and non-polar solvents are used to investigate the electronic solvation properties of the title compound using the TD-DFT/IEFPCM model (M062X for UV–Vis and B3LYP for NBO, NLO, HOMO-LUMO, MEP). The occurrence of charge transfer in a molecule is explained by Natural Bond Orbital (NBO) analysis. The local reactivity descriptor describes the reactive regions of the molecule. The title compound's kinetic stability and reactivity are demonstrated using thermodynamic and Frontier Molecular Orbital (FMO) functions. The substance under research has excellent NLO properties. For the head compound, topological analyses such as ELF, LOL and RDG are performed and reported. The biological features (drug-likeness, toxicity and ADME) are calculated, which reveals the pharmaceutical activities of the compound. Molecular docking studies are used to investigate ligand–protein interactions, to show the insulin inhibitor activity of the chemical under research.